A pressure control valve for use in railway car brake systems is shown and disclosed in my copending U.S. patent application Ser. No. 07/278,518, concurrently filed herewith, and one embodiment will presently be explained with reference to the accompanying FIGS. 3 and 4 of the drawings. It will be noted that the pressure control valve shown in FIGS. 3 and 4 includes a middle body member 31 and a main piston 32 located in the main valve body 30. The valve includes an air supply chamber 41, an output chamber 42, an exhaust chamber 43, an air supply valve 44, an exhaust valve rod 45, a balance piston 46, and a control piston 47.
The external shape of the middle body 31 takes the form of a short cylinder which is fitted and situated in the inner opening 48 formed in the upper part of the main valve body 30 so that it can be shifted vertically or moved up and down therein. As shown, the air supply chamber 41 is formed in the middle body member 31, and there is a valve seat 50 at the air supply passage 49 which extends downwardly toward the outlet chamber 42. The air supply valve 44 is located in the member 31 and is biased by the compression spring 51 so that it is urged onto the valve seat 50. The air supply chamber 41 is connected to a suitable source of air pressure via a supply passage 52 which is formed in the right side of the main valve body 30, as shown in FIG. 3. The air supply chamber 44 is provided with a central vent passage 54 which leads the back vent chamber 53 formed at the top thereof. The bottom of the passage 54 ends in the vicinity of the air supply passage 49.
The lower end of the middle body member 31 communicates with the output chamber 42. The output chamber 42 is connected to the brake cylinder of the brake system via the delivery passage 55 formed in the main valve body 30 as shown in FIG. 3. A vent passage 56 is connected from the output chamber 42 to the space located above the middle body member 31, namely, the vent chamber 48. Alternately, the vent chamber 48 can be opened to the atmosphere via a vent hole which may be formed in the top of the main valve body 30 so that the passage 56 may be omitted.
As shown in FIG. 3, an adjusting screw 57 may be screwed into a threaded hole formed in the top of the main valve body 30. The exterior of the screw 57 may be manually turned and adjusted to a desired position. A biasing spring 58 engages the underside of the middle body member 31 and urges the body member 31 upwardly against the tip of screw 57. That is, the rotatable screw 57 fits into the top of the main valve body 30 and extends from the outside to the inside of the inner chamber 48 so that its tip touches the top of the middle body member 31. As shown, the compressed return spring 58 is caged between the main piston 32 and the middle body member 31. Thus, the middle body member 31 can be moved to the desired position simply by rotating the screw 57 from outside which together with the biasing spring 58 fixes it in that position.
The main piston 32 is positioned in the internal opening 59 formed in the lower section of the main valve body 30. The main valve body 30 consists of the balance piston portion 60 which is integral with the lower end of the exhaust valve rod 45. The main valve body 30 also includes a control piston portion 61. Thus, the balance piston 46 includes the portion 60 and a flexible diaphragm 62 which has its inner periphery attached to the piston portion 60 and has its outer periphery attached to the wall of the internal opening 59. Similarly, the control piston 47, includes portion 61 and a flexible diaphragm 63 which has its inner periphery attached to the piston portion 61 and has its outer periphery attached to the wall of the internal opening 59. A first plurality of radially extending fins 64 are attached to the main body 32 while a second plurality of radially extending fins 65 are attached to the inner wall of the opening 59. It will be seen that the fins 64 include upper edges 74 while the fins 65 include upper edges 75.
The flared rim or valve tip 66 of the exhaust valve rod 45 is located adjacent the air supply valve 44 on the side of the output chamber 42. The outside diameter of the periphery of the valve tip 66 is essentially equal to the inside diameter of the rear chamber 53 formed above the air supply valve 44. As shown in FIG. 3, the exhaust valve rod 45 is provided with an exhaust port 67. One end of the exhaust hole 67 opens at the valve tip 66 and the other end opens at the exhaust chamber 43 which is opened to the atmosphere via exhaust passage 72.
As shown, the lower portion of the exhaust valve rod 45 is integrally formed by a guide and stabilizing collar 68 which is joined to the balance piston main body 60 and the control piston main body 61 moves in unison with the exhaust valve rod 45. In viewing FIG. 3, the direction of movement is in a vertical manner, and the lower collar 68 fits into the lower guide portion 76 of the main valve body 30 so that it can freely slide therein. As noted above, the inner rim of the diaphragm 62 is attached to the outside circumference of the balance piston main body 60 while the outer rim or periphery is attached to the inner wall of the internal opening 59 of the main valve body 30. In addition, the inner rim or periphery of the diaphragm 63 is connected to the lower extremity of the control piston main body 61 while the outer rim or periphery is attached to the inner wall of the internal opening 59 of the main valve body 30. Preferably, these diaphragms 62 and 63 are made of flexible rubber-like material. The inside of the internal opening 59 is divided into a balance chamber 69, the exhaust chamber 43, and a control chamber 70 as viewed from the top in FIG. 3. The chambers 69, 43 and 70 are made air tight by the diaphragms 62 and 63. The balance chamber 69 is connected to the output chamber 42 by a passage 71. The exhaust passage 72 is connected to the exhaust chamber 43 which passes through the outer left wall of the main valve body 30. The control passage 73 into which the control air pressure is introduced is fed to the control chamber 70. The passage 73 is formed in the outer right wall of the main valve body 30. As previously noted, the first fins 64 are formed on the outer circumference wall of the balance piston main body 60 and extend in the radial direction, as shown in FIG. 4. The outer edges of fins 64 extend nearly to the inner surface of the internal opening 59. The upper edges 74 which face the diaphragm 62 form a straight inclined downwardly and outwardly surface as shown in FIG. 3. The second radial fins 65 extend from the wall of the internal opening 59 of the main valve body 30, as can be seen in FIG. 4. The second fins 65 enter or interleave between each of the first fins 64. The upper edge 75 which is adjacent the underside of the diaphragm 62 forms a straight surface which inclines downwardly and inwardly as shown in FIG. 3. The upper edges 74 of the first fins 64 and the upper edges 75 of the second fins 65 are interposed between the balance piston main body 60 and the wall of the internal opening 59. This intersection line between the fins forms a concentric circle with the balance piston main body 60 so that the diameter of the circle of the intersection line changes with the movement of the piston main body 60 in the axial direction.
As indicated in FIG. 3, the pressure control valve is in an overlap condition. In the overlap state, the valve tip 66 of the exhaust valve rod 45 is in contact with the air supply valve 44, and at the same time the air supply valve 44 seats on the valve seat 50. In other words, the output chamber 42 is shut-off from the air supply chamber 41 and also from the exhaust chamber 43.
In this overlap state, when the control air pressure P1 in the control chamber 70 is reduced, the control force exerted by the control piston 47 becomes less than the balance force exerted by the balance piston 46 so that the piston 32 moves downwardly as viewed in FIG. 3. When the valve tip 66 of the exhaust valve rod 45 moves away from the air supply valve 44, the output chamber 42 becomes opened to the atmosphere via the exhaust hole 67 and the exhaust chamber 43. By this exhausting action, the output air pressure P2 in the output chamber 42 decreases. Now when the balance force drops and reaches equilibrium with the control force, it again resumes the overlap state. When the control air pressure P1 is decreased to atmospheric pressure, the output air pressure P2 also becomes atmospheric pressure.
In the overlap condition, when the control air pressure P1 increases, the control force becomes greater than the balance force, and the piston 32 moves upwardly as shown in FIG. 3. The exhaust valve rod 45 pushes upwardly and causes the air supply valve 44 to be separated from the valve seat 50. Thus, the air pressure is supplied from the air supply chamber 41 to the output chamber 42 via the air supply passage 49. After the output air pressure P2 rises as a result of this air pressure, and when the balance force increases to balance with the control force, it again reverts to the overlap condition.
Thus, with this pressure control valve, the output air pressure P2 can be made to correspond to P1 simply by changing the control air pressure P1. As noted above, the output air pressure P2 may be used to operate a vehicle brake system.
The presently described pressure control valve is characterized by the fact that the output air pressure P2 is controlled by the control air pressure P1 which can be changed by moving the position of the middle body member 31 vertically as shown in FIG. 3.
The effective area of the control piston 47, which includes the control piston main body 61 as well as the diaphragm 63, is S1 while the effective area of the balance piston 46, which includes the balance piston main body 60 and the diaphragm 62, is S2. When it assumes the overlap state indicated after the control air pressure P1 has been exerted on the control chamber 70, then the output air pressure P2 in the output chamber 42, can be indicated by the following equation: EQU P2=(S1/S2).times.P1
since the force of the return spring 58 is less than the force of the piston caused by the air pressure.
Here, the effective area S2 of the balance piston is the area where the cross-sectional area of the valve tip 66 and the exhaust hole 67 of the exhaust valve rod 45 is subtracted from the area inside the circle of the above-mentioned intersecting line. In other words, inside the above-mentioned intersection line, the diaphragm 62 touches the first radial fins 64 extending from the balance piston main body 60. The force due to the pressure in the balance chamber 69 is transferred to the balance piston main body 60 inside this circle. However, outside this circle, it contacts the second radial fins 65 protruding from the main valve body 30, so that the work force due to the pressure of the balance chamber 69 is transferred to the side of the main valve body 30 and does not reach the balance piston main body 60.
This pressure control valve can change the effective area S2 of the balance piston by moving the position of the middle body member 31 by the adjusting screw 57. In other words, the position of the middle body member 31 can be changed by rotating the adjusting screw 57 so that it moves member 31 vertically. For example, if the adjusting screw 57 is moved upward, the middle body member 31 is moved upwardly by the force of the biasing spring. If the middle body member 31 is raised to the position indicated by the phantom line 31a, the valve tip 66 of the exhaust valve rod 45 rises that much in order to retain the overlap condition, so that the balance piston main body 60 which is integrally connected to the exhaust valve rod 45 and the control piston main body 61 also rises. Therefore, in the overlap condition after the position of the middle body member 31 has changed, the diameter of the circle of the intersection line related to the effective area S2 of the above-mentioned balance piston increases so that the effective area S2' becomes larger than the previous effective area S2. The character 64a shows the position of the first radial fins in the overlap condition after the position of the middle body member 31 has been changed.
The change of the effective area of the balance piston from S2 to S2' means that the above-mentioned effective area ratio S1/S1 will be changed to S1/S2' so that the characteristic of the output air pressure P2 in relation to the control air pressure P1 can be varied.
In the above-mentioned pressure control valve, the upper edges 74 and 75 of the corresponding first and second radial fins 64 and 65 adjacent the underside of diaphragm 62 slope in a downward direction. However, in practice one of the upper edges 74 or 75 of the fins can be disposed horizontally, namely, in the direction perpendicular to the axis of the piston 32. In other words, in any case, the effective area of the balance piston 46 in the overlap condition can be varied by changing the position of the middle body member 31, and the effective area ratio of control piston 47 and the balance piston 46 can be modified.
In addition, instead of the structure in which the fins are placed on the side of the main valve body 30 corresponding to the balance piston main body 60, the equivalent of the first fins 64 and the second fins 65 can be placed adjacent the side of the control piston 47, or they can be provided on both sides so that the effective area ratio of the control piston 47 and the balance piston 46 can be changed in the same way.
As shown in FIG. 4, the diaphragm 62 is in contact with the upper edges of the first fins 64 and the second fins 65 of the pressure control valve. That is, the air pressure on the upper side of the diaphragm 62 pushes the underside against the upper edges of the fins 64 and 65. Thus, the diaphragm 62 is deformed so that it takes on an undulating shape. The concave and convex portions of this wave shape are opposite on either side of a boundary which is the circle 77 of the intersecting line. The inner peripheral surface of the diaphragm 62 engages the upper edges 74 of the first fins 64 and the outer peripheral surface of the diaphragm 62 engages the upper edges 75 of the second fins 65. Thus, the diaphragm 62 is supported by the first fins 64 on one side of circle 77 and is supported by the second fins 65 on the other side of circle 77. In other words, a space exists between the first fins 64 on the one side and a space exists between the second fins 65 on the other side. Thus, the diaphragm 62 is a wavy portion approximately along the circle 77 of the intersecting line. This bending or undulating strip straddles the inside and the outside sections of the circle 77 of the intersecting line due to the existence of the wave as represented by the curved line 76 in FIG. 4. It will be appreciated that the position of the wave band 76 changes in the radial direction, as the diameter of the circle 77 of the intersecting line is increased or decreased due to the movement of the piston 46. The change in position is caused when the diaphragm is deformed into a wave form which tends to be pushed into the existing space between the fins 64 and 65 so that a relatively large deformation resistance is encountered. This deformation resistance is added to the displacement resistance of the piston 46 so that the ability of the output air pressure to quickly respond to the control air pressure is hindered which is a disadvantage.